pfsin: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/pfsin - from package: pfstools

You may install the required package with command apt-get install {package}

Error in other languages:
pfsin: bevel nie gevind nie
pfsin: comandă negăsită
pfsin: comando não encontrado
pfsin: commande introuvable
pfsin: command not found
pfsin: käsku ei ole
pfsin: không tìm thấy lệnh
pfsin: komanda nerasta
pfsin: Kommando nicht gefunden.
pfsin: kommandot finns inte
pfsin: komut yok
pfsin: nie znaleziono polecenia
pfsin: níor aimsíodh an t-ordú
pfsin: no se encontró la orden
pfsin: no s'ha trobat l'ordre
pfsin: opdracht niet gevonden
pfsin: parancs nem található
pfsin: perintah tidak ditemukan
pfsin: príkaz nenájdený
pfsin: příkaz nenalezen
pfsin: команда не найдена
pfsin: командата не е открита
pfsin: 命令找不到
pfsin: コマンドが見つかりません